Research Progress of Cryogenic Materials for Storage and Transportation of Liquid Hydrogen

Round 1

Reviewer 1 Report

Comments to Review Article: „Research Progress of Cryogenic Materials for Storage and Transportation of Liquid Hydrogen.

This review article deals with an overview of different materials and their qualification to use them for storage and transportation of liquid hydrogen.

Here types of stainless steel, types of Aluminum alloy, Titanium alloy and composites suitable for cryogenic temperatures are described.

These descriptions are well done and backed up with literature.

But the main aim of the article is to emphasize the fundamental need for further research in the field of materials with regard to their hydrogen compatibility. The need for liquid hydrogen storage containers and transport lines for a wide variety of stationary and mobile applications will increase rapidly and a fundamental understanding of the suitability of the materials to be used and the development of new materials is fundamental for the construction of these containers and lines.

Apart from this correct analysis, the authors see a deficit of research and knowledge in this area in China and explain that many values are known, for example in the USA, but are not published.

This article is above all an appeal to China to advance research in this important area. One can understand this on the one hand as a kind of research proposal or as an appeal to those responsible for the funding of such research work.

The question here is therefore whether this article is suitable for an international journal. One suggestion here for an international journal would be to omit the national reference and only emphasize the international need for research and publication.

See comments in the attached file.

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 1 Comments

Comments to Review Article: Research Progress of Cryogenic Materials for Storage and Transportation of Liquid Hydrogen.

Point 1: This review article deals with an overview of different materials and their qualification to use them for storage and transportation of liquid hydrogen.

Here types of stainless steel, types of Aluminum alloy, Titanium alloy and composites suitable for cryogenic temperatures are described.

These descriptions are well done and backed up with literature.

Response 1: Thank you for your good comments on our article.

Point 2: But the main aim of the article is to emphasize the fundamental need for further research in the field of materials with regard to their hydrogen compatibility. The need for liquid hydrogen storage containers and transport lines for a wide variety of stationary and mobile applications will increase rapidly and a fundamental understanding of the suitability of the materials to be used and the development of new materials is fundamental for the construction of these containers and lines.

Response 2: We agree with you. The increasing application of liquid hydrogen will promote the needs of fundamental understanding of the suitability of the materials. Therefore, we want to review the study progress of cryogenic materials. As a result of providing some guidance for the study and application of cryogenic materials used for storage and transport of liquid hydrogen.

Point 3: Apart from this correct analysis, the authors see a deficit of research and knowledge in this area in China and explain that many values are known, for example in the USA, but are not published.

Response 3: Because it is difficult to test the material properties at liquid hydrogen temperature, the data at this cryogenic temperature is relatively scarce in China.

Point 4:This article is above all an appeal to China to advance research in this important area. One can understand this on the one hand as a kind of research proposal or as an appeal to those responsible for the funding of such research work.

The question here is therefore whether this article is suitable for an international journal. One suggestion here for an international journal would be to omit the national reference and only emphasize the international need for research and publication.

 Response 4: In fact, our main purpose is to systematically review the cryogenic materials used in liquid hydrogen temperature region, so as to provide reference for the research and practical application of cryogenic materials. We have reduced the content about the introduction of the situation in China. Liquid hydrogen has attracted much attention in recent years, however, the complete reviews about the materials for its storage and transport is very lack. We have revised the manuscript, which increased the international need for research and publication.

Point 5: See comments in the attached file.

Response 5: We have revised the manuscript according to your comments. However, we have choose not to add “in China” to the title of the article. We reduce the introduction of China's research status in the article, and increase the relevant research results, hoping to be more suitable for an international journal.

Author Response File: Author Response.pdf

Reviewer 2 Report

Cryogenic transport of hydrogen experiences an increased interest since the use of hydrogen produced by wind and solar power (green hydrogen) is extensively discussed in the western world. Surprisingly enough this is not mentioned in the review.

1. The paper gives quite a general review of the use of cryogenic materials. According to the authors’ opinion the knowledge about the topic is limited in China. It is unlikely that the knowledge is less than in many other countries.
2. It is understandable that some types of companies are reluctant to publish data on cryogenic materials. However, for example car producers would be more likely to inform about their materials when they are involved with liquid hydrogen. Otherwise it would be difficult for them to get customers.
3. The reader gets the impression that a significant part of text is intended as an application for research money for the authors. This should be reduced to a small part.
4. The assumed state of knowledge seems to be used as an excuse that more material cannot be presented. This should definitely be avoided.
5. In the review very limited facts are presented. There is only one table and no figures. Many major statements made in the paper should be illustrated with figures or tables.
6. Property data at liquid nitrogen temperatures can be considered. In practice, it is very difficult to make mechanical tests at still lower temperatures without getting an uncontrolled large increase in temperature.
7. In particular, it is important that critical properties in cryogenic applications such as ductility and impact toughness are exemplified for the materials groups covered.
8. The statement that the ductility is in general increased with reduced temperature should be removed. It depends on how the work hardening is changed with temperature.
9. A comment about austenitic stainless steels: The most important feature is that the material is free from ferrite and martensite in cryogenic applications.
10. In the description of aluminum alloys, all types seem to be applicable to low temperature service. It is at least likely that alloys suitable for friction stir welding would be of prime interest.

Author Response

Response to Reviewer 2 Comments

Cryogenic transport of hydrogen experiences an increased interest since the use of hydrogen produced by wind and solar power (green hydrogen) is extensively discussed in the western world. Surprisingly enough this is not mentioned in the review.

Point 1: The paper gives quite a general review of the use of cryogenic materials. According to the authors’ opinion the knowledge about the topic is limited in China. It is unlikely that the knowledge is less than in many other countries.

 Response 1: Our main purpose is to systematically review the cryogenic materials used in liquid hydrogen temperature region, so as to provide reference for the research and practical application of cryogenic materials. As you mentioned, we indeed should not give too much introduction about the situation of any country. We have revised the manuscript with reducing the content of this introduction and adding more international researches.

Point 2: It is understandable that some types of companies are reluctant to publish data on cryogenic materials. However, for example car producers would be more likely to inform about their materials when they are involved with liquid hydrogen. Otherwise it would be difficult for them to get customers.

Response 2: We agree with you that some companies are more likely to publish their material data. However, liquid hydrogen is used in aerospace field more widely in recent years, and some data maybe restricted. Furthermore, it is not so convenient for testing cryogenic properties of materials at the liquid hydrogen temperature, the data at this cryogenic temperature is relatively scarce.

Point 3: The reader gets the impression that a significant part of text is intended as an application for research money for the authors. This should be reduced to a small part.

Response 3: We have reduced the introduction of the China's current situation about the research of cryogenic materials.

Point 4: The assumed state of knowledge seems to be used as an excuse that more material cannot be presented. This should definitely be avoided.

Response 4: We have revised the manuscript with adding more objective research results and reducing the assumed state of knowledge.

Point 5: In the review very limited facts are presented. There is only one table and no figures. Many major statements made in the paper should be illustrated with figures or tables.

Response 5: We have added more figures and tables.

Point 6: Property data at liquid nitrogen temperatures can be considered. In practice, it is very difficult to make mechanical tests at still lower temperatures without getting an uncontrolled large increase in temperature.

Response 6: We agree with you that the mechanical tests at liquid hydrogen temperature is difficult.

Point 7: In particular, it is important that critical properties in cryogenic applications such as ductility and impact toughness are exemplified for the materials groups covered.

Response 7: We have exemplified the ductility and impact toughness of the materials groups covered in the revised manuscript.

Point 8: The statement that the ductility is in general increased with reduced temperature should be removed. It depends on how the work hardening is changed with temperature.

Response 8: We have removed the statement that the ductility is in general increased with reduced temperature should be removed.

Point 9: A comment about austenitic stainless steels: The most important feature is that the material is free from ferrite and martensite in cryogenic applications.

Response 9: We agree with you that the most important feature is that the material is free from ferrite and martensite in cryogenic applications.

Point 10: In the description of aluminum alloys, all types seem to be applicable to low temperature service. It is at least likely that alloys suitable for friction stir welding would be of prime interest.

Response 10: We agree with you that all types of aluminium alloys have good cryogenic ductility and impact toughness, which can be applied to cryogenic temperature. So, other properties such as weldability, corrosion resistance and also specific strength should be considered at first when use in specific environments.

Author Response File: Author Response.pdf

Reviewer 3 Report

- although listed in the paper, there are not numerical values reported in the introduction concerning physical quantities in  terms of  ranges to be reached in the search of materials in liquid hydrogen storage (e.g. the specific heat capacity, coefficient of linear expansion, Young's modulus and thermal conductivity). May you provide which kind of numbers are to be expected? Please also provide which are the requirements of low temperature storage and transportation containers of liquid hydrogen, for clarity and completeness.

- "For materials without low-temperature brittle transition, the elongation increases with the
decrease of temperature."-> please provide numbers and references (the same as in [21]?)

- how do these materials effect the ortho-to-para ratio for liquid hydrogen and hence the decrease of heat connected to these problem? There is no reference in the paper 

- please rephrase "The tensile property can evaluate the tensile strength, yield strength, elastic modulus and plasticity index of materials.", not clear

- I would move the generic info on the atomistic level behaviour provided in Section 2.3. "Cryogenic mechanical properties of stainless steel" in the Intro

- please provide information and requirements concerning the weights

- "Titanium alloy has been widely used in aerospace field due to its advantages of high specific strength, good corrosion resistance, high temperature resistance, low thermal conductivity and small coefficient of expansion. In addition, titanium alloy has excellent cryogenic performance."-> please provide numbers and refs

- (20k), -> (20 K) (in the intro + line 359)
- are summarized To -> are summarized to
- Y. H. fan [14] -> Fan
- add . at the end  of "Pure titanium has a close packed hexagonal structure at room temperature α" and "With the decrease of temperature, the plasticity and toughness of the phase decrease "
- "The Russia" ->  Russia
- "Russia was at the leading level in the world in the research and development of low-temperature titanium alloys and developed a series of low aluminum low-temperature titanium alloys, among which OT4 and BT5-1 are widely used. " -> please provide refs

Author Response

Response to Reviewer 3 Comments

Point 1: Although listed in the paper, there are not numerical values reported in the introduction concerning physical quantities in  terms of  ranges to be reached in the search of materials in liquid hydrogen storage (e.g. the specific heat capacity, coefficient of linear expansion, Young's modulus and thermal conductivity). May you provide which kind of numbers are to be expected? Please also provide which are the requirements of low temperature storage and transportation containers of liquid hydrogen, for clarity and completeness.

Response 1: The critical properties in liquid hydrogen are ductility, impact toughness and compatibility. The physical quantities such as the specific heat capacity, coefficient of linear expansion, Young's modulus and thermal conductivity also have some influences in the application. However, considering the limited space, this article mainly focuses on the introduction of mechanical properties at low temperature. So the physical properties will be reviewed in our future work.

Point 2:  "For materials without low-temperature brittle transition, the elongation increases with the decrease of temperature."-> please provide numbers and references (the same as in [21]?)

Response 2: We have provided numbers and references. It is the same as in  [21].

Point 3: how do these materials effect the ortho-to-para ratio for liquid hydrogen and hence the decrease of heat connected to these problem? There is no reference in the paper 

Response 3: The ortho-to-para ratio for liquid hydrogen can be affected by materials. However, this article mainly focuses on the cryogenic mechanical properties of materials used in liquid hydrogen. So we have no introduction in this aspect. We will review this content in our future work.

Point 4: please rephrase "The tensile property can evaluate the tensile strength, yield strength, elastic modulus and plasticity index of materials.", not clear

Response 4: We have rephrased the sentence as below: “The tensile strength, yield strength, elastic modulus and plasticity index of materials can be obtained by tensile test.”

Point 5: I would move the generic info on the atomistic level behaviour provided in Section 2.3. "Cryogenic mechanical properties of stainless steel" in the Intro

Response 5: We have moved the statements about the atomistic level behaviour provided in Section 2.3.

Point 6: - please provide information and requirements concerning the weights

Response 6: Different applications have different requirements for weight, but for aerospace, it is the future trend to reduce the weight as much as possible when meeting the conventional performance requirements.

Point 7: - "Titanium alloy has been widely used in aerospace field due to its advantages of high specific strength, good corrosion resistance, high temperature resistance, low thermal conductivity and small coefficient of expansion. In addition, titanium alloy has excellent cryogenic performance."-> please provide numbers and refs

Response 7: We have provided numbers and references.

 Point 7: - (20k), -> (20 K) (in the intro + line 359)

Response 7: We have revised 20k into 20 K.

Point 8: - are summarized To -> are summarized to

Response 8: We have revised “are summarized To” into “are summarized to”.

Point 9: Y. H. fan [14] -> Fan

Response 9: We have revised “Y. H. fan” into “Fan” in Reference [14].

Point 10: add . at the end  of "Pure titanium has a close packed hexagonal structure at room temperature α" and "With the decrease of temperature, the plasticity and toughness of the phase decrease "

Response 10: We have added . in the two sentences.

Point 11: "The Russia" ->  Russia

Response 11: We have revised “The Russia” into “Russia”.

Point 12: "Russia was at the leading level in the world in the research and development of low-temperature titanium alloys and developed a series of low aluminum low-temperature titanium alloys, among which OT4 and BT5-1 are widely used. " -> please provide refs

Response 12: We have provided the references.

Author Response File: Author Response.pdf